Sandstone Surface Research Articles

Evaluating the Protective Effects of Calcium Carbonate Coating on Sandstone Cultural Heritage

The purpose of this work was to use different surfactants to deposit different crystalline calcium carbonate films on the surface of sandstone through a simple double displacement reaction. This was done to test the protective effects of calcium carbonate coatings based on water absorption, moisture permeability and weather resistance. Experimental results showed that the air permeability of the stone treated with vaterite calcium carbonate was reduced, but that this did not affect water vapor’s access into and out of the stone. Compared with untreated stone, the water absorption rate was reduced 0.5 times, and the weather resistance increased by 4 times due to small crystal grains, high solubility, and deep penetration hindering the erosion of water and soluble salts. These findings are expected to provide useful suggestions for the protection of stone cultural heritage.

Research on the relationship between anti-skid performance and various aggregate micro texture based on laser scanning confocal microscope

The micro-texture of the aggregate plays a very important role in the anti-skid performance of the asphalt pavement. Currently, the polished stone value (PSV) index is mostly used for the characterization of the aggregate, but the micro-texture is rarely considered. In addition, there are few studies that compares micro-textures of different aggregates and their relationship with PSV. In this study, eight different aggregates were selected, including three types of sandstone, limestone, basalt, diabase, gabbro and granite. The PSV and micro-texture of the aggregates during the polishing process were tested by the british pendulum tester (BPT) and the laser scanning confocal microscope (LSCM) respectively, and the relationship between PSV and the micro-texture was regressed. Finally, scanning electron microscope (SEM) images were generated and used to explain the reason for the texture differences in the aggregate from the perspective of the micro-structure. It was found that there was no significant difference on the anti-skid performance of the aggregates before polishing. SEM images showed an unevenness on the surface of sandstone with lots of pits, which is conducive for long-term maintenance of texture. Consequently, sandstone had the best anti-skid performance after polishing, followed by magmatic rock, and limestone. Although, polishing effect reduces the micro-texture of the aggregates, but the micro-texture of the sandstone aggregate was not significantly affected before and after polishing. Overall, the texture of arkose was the largest, followed by red sandstone, quartz sandstone, granite, diabase, gabbro, basalt, limestone. There is an obvious correlation between the micro-texture and the anti-skid performance of the aggregate. The aggregates had better anti-skid performance when the micro-texture index Ra was kept above 4 μm. The multiple linear equation between micro-texture and PSV is obtained by regression analysis, which can be used to predict the PSV of the aggregate. Based on the findings from this study, sandstone is highly recommended as the first choice aggregate for anti-skid performance, followed by magmatic rock and finally limestone.

Characterization and origin of the Mn-rich patinas formed on Lunéville château sandstones

Abstract. The formation of iron- and/or manganese-rich dark patinas on sandstones is a common natural phenomenon that occurs also on building stones. Lunéville château, in eastern France, presents such patinas that developed either under natural conditions (rain and time) or after an accidental fire and exposure to significant amounts of water as part of attempts to extinguish the fire. The present study aimed at characterizing both types of patinas in an effort to determine their formation mechanisms and Mn sources. In both cases, Mn required for patina formation likely derives from the reductive dissolution of Mn-rich minerals present in pristine sandstones, as suggested by the contrasting mineralogy and chemistry of Mn-rich phases present in the bulk and in the patina of a given building block. Reduced Mn species then migrate to the exposed surface of building blocks where they are re-oxidized via undetermined processes. Patinas developing “naturally” over time result from the alternation of wetting-reducing and drying-oxidizing cycles and appear to be composed of birnessite. Patinas formed after the 2003 fire result from this single accidental event and form a much thinner, heterogeneous, and discontinuous layer of poorly crystalline lithiophorite at the sandstone surface (∼ 0–150 µm compared to ∼ 300–600 µm for “natural” patinas). The lack of Mn-rich patinas on areas of Lunéville château is likely related to the lower Mn content of pristine sandstone blocks.

Favorable and unfavorable attachment of colloids in a discrete sandstone fracture

The transport of cationic amine-modified latex (AML) and anionic carboxylate-modified latex (CML) microspheres through a discrete sandstone fracture with mineralogical heterogeneity and roughness was studied. Two microsphere sizes (200 nm and 1000 nm), two ionic strengths (5 mM and 10 mM), and two specific discharges (0.35 mm.s-1 and 0.70 mm.s-1) were tested to observe the impact on transport under favorable and unfavorable conditions. The difference in retention between AML (net favorable) and CML (net unfavorable) microsphere attachment was 25% for the 200 nm microspheres and 13% for the 1000 nm microspheres. Less than 50% of the AML microspheres were retained in the fracture, postulated to be due to the effects of mineralogical heterogeneity and fracture surface roughness. The effect of an increase in ionic strength in increasing retention was significant for unfavorable attachment, but was not significant for favorable attachment conditions. The effect of specific discharge was minor for all but the 200 nm CML microspheres at 10 mM ionic strength. When flushing the fracture first with cationic microspheres, then with anionic microspheres, the recovery of anionic microspheres resembled favorable attachment presumably due to interaction with cationic microspheres that remained attached to the sandstone surface. Colloid breakthrough curves could be fit well with a two site attachment model, with reversible and irreversible sites.

Molecular dynamics simulation of the interfacial wetting behavior of brine/sandstone with different salinities

At present, the mechanism of the influence of salinity on wettability of reservoir rocks is still insufficient. In this paper, molecular dynamics simulation is used to study the wetting behavior of water droplets on the surface of sandstone under different salinities, and the system equilibrium configuration is used to analyze the interaction among the components of the system. To clarify the mechanism of the influence of ions on the wetting of water droplets on the sandstone surface, the distribution characteristics of anions and cations, ion hydration and the association between anions and cations in the equilibrium system were analyzed. The influence of salinity on the wettability of water droplets on the sandstone surface is comprehensively evaluated by calculating the average interaction potential between ions and water molecules, the change in cohesive energy density among particles in the brine system and the change in the number of hydrogen bonds among water molecules.

An internal recycling mechanism between ammonia/ammonium and nitrate driven by ammonia-oxidizing archaea and bacteria (AOA, AOB, and Comammox) and DNRA on Angkor sandstone monuments

The ancient Angkorian sandstone monuments in Cambodia are well known for biodeterioration of the sandstone under tropic climate. This study examined ammonia oxidizing bacteria (AOB and Comammox) and archaea (AOA) in stone-dwelling microbiome from three important Angkor monuments, namely Angor Wat, Bayon of Angkor Thom, and Preah Vihear, by DNA-based metagenomics analysis, RNA-based functional gene reverse-transcriptional (RT)-qPCR quantification, and N-15 isotope analysis. Our metagenomics datasets on these three monuments reveal a rich microbiome and abundant microbial nitrogen transforming reactions of ammonia oxidation and nitrite oxidation, Comammox and dissimilatory nitrate reduction to ammonium (DNRA), and these results support an internal recycling mechanism between ammonia/ammonium and nitrate by AOA, AOB, Comammox and DNRA on the stone monuments to support the microbial community. Though a wide range of AOB and AOA lineages together with Comammox were retrieved from these metagenomes as the potential ammonia-oxidizers, only AOA and Comammox were most abundant, likely to contribute to the biochemical processes of ammonia oxidation. The RNA-based qPCR quantification of the functional gene amoA in this study showed that AOA were the more active ammonia oxidizers over AOB in the microbiome of these Angkor sandstone monuments. In addition, a rich population of nitrite/nitrate producing AOA and Comammox drove the sequestration of CO2 onto the stone and this process was in turn supported by DNRA to provide the substrate ammonia/ammonium for a further cyclic reaction to take place continuously between ammonia/ammonium and nitrate. This model is further supported by the high enrichment of stable isotope 15N signature of NO3− in sandstone surface biofilms. The findings of this study are insightful for elucidation of nitrate accumulation by an internal N cycling mechanism proposed, and are important for understanding the sustainable microbial community and protection management of stone cultural heritage.

Study on Nano-Materials Improving Fracturing Fluid Performance and Oil Displacement Mechanism

Because of its characteristics and advantages, nano-materials can significantly improve the performance of fracturing fluid after being added to fracturing fluid. The research on the action mechanism of nano-materials in fracturing fluids is the theoretical basis and basis for developing functional fracturing fluids. At the nanoscale (50nm), SiO2 was modified with C8 and quaternary ammonium salt (QAS),synthesizing the Hydrophobic nano-materials SiO2-C8 and hydrophobic charged nanomaterials SiO2-QAS .The dispersion method, addition amount, compatibility stability and rheological properties of SiO2, SiO2-C8 and SiO2-QAS nano-materials in SRFP clean fracturing fluid system were studied. By means of quantitative simulation methods, the adsorption structure model and adsorption kinetics of nano-materials on sandstone surface were established The model analyzes the adsorption and oil-water separation characteristics of nano-materials on the sandstone surface. The research results show that the three nano-materials have better dispersion stability in the clean fracturing fluid, can effectively reduce the surface tension of the fracturing fluid, and show better temperature and shear resistance; Due to the special adsorption characteristics and specific interface effects of SiO2-C8 and SiO2-QAS nano-materials, which are beneficial to the replacement of oil molecules on the sandstone surface after the addition of fracturing fluid, and promote the separation of oil and water. The addition of SiO2-C8 and SiO2-QAS nano-materials can effectively improve the performance of fracturing fluid, improve the oil displacement effect on the surface of sandstone, and achieve the purpose of reducing oil saturation and increasing the fluidity of crude oil within the range of fracturing fluid. The results can be used as a reference for the development of functional fracturing fluid and the progress of fracturing technology for tight oil and shale oil.

Infrared radiation test on the influence of water content on sandstone damage evolution

The rock mechanics uniaxial compression testing system and a thermal imaging camera were used to research the influence of water on sandstone damage evolution and the concurrent infrared radiation (IR) characteristics on sandstone samples with different water contents. The field of view of the thermal imaging camera divided the sandstone surface into several small areas of equal area. When one of the small areas of sandstone ruptured (that was when a damage point was generated in the sandstone) the IR information from that area underwent abrupt changes. Based on this monitoring, a quantitative index of infrared radiation, the IR count (IRC), was adopted and investigated as the indicator for damage evolution of rocks that also linked damage intensity with the corresponding IR temperature. The research results showed that when the sandstone stress experienced a stress drop, the IRC will simultaneously undergo a sudden increase indicating that the IRC was controlled by the stress. However, this stress control on IRC decreased with increasing water content due to the softening effect of water on the sandstone. Among them, the control effect of stress on IRC reaches 100% for dry sandstone, which is reduced to 75% for sandstone with a water content of 0.5% and 66.7% for sandstone with a water content of 1.5%. The control effect of stress of saturated sandstone on IRC is 57.1%. For sandstones with other water contents, but at the same damage evolution stage, the average IRC (IRC¯) for sandstones showed an upward trend as the water content increased. Compared with other damage evolution stages, the IRC¯ of the water-bearing sandstone had the most significant difference in the failure stage, indicating that water had the most significant influence on the damage evolution of the sandstone in the failure stage. This IRC was generated at the location of a new damage point on the sandstone surface. Therefore, based on the instant of time node when the sandstone IRC suddenly increased, the IRC spatial distribution map at that corresponding time was drawn to accurately locate the sandstone damage and fracture area. The characteristics of the damage evolution process of sandstones with different water contents were the same over the time before the sudden increase in IRC, the damage points formed were disorderly distributed, and the number of damage points was less. The difference was that as the water content increased, the number of sandstone damage points became larger and more concentrated.

Evaluation of a new green synthesized surfactant from linseeds - chemical EOR implications from sandstone petroleum reservoirs

Surfactants are materials with different applications in industries. The development of surfactants and the reduction in their associated harmful effects are among the most crucial matters that must be taken into account to increase their efficiency. Surfactants are widely employed in chemical enhanced oil recovery, yet sometimes these materials are not environmentally friendly and economically affordable. Hence, the natural surfactants were introduced to address this issue. However, they show poor efficiency in the main mechanisms of oil recovery enhancement, including wettability alteration and interfacial tension reduction. Herein, a new anionic surfactant was synthesized from the natural base material (linseeds) revealing high efficiency in chemical enhanced oil recovery. In addition, esterification and sulfonation methods were applied to conduct the synthesis process. Following the conduction of the synthesis process, the synthesized surfactant was characterized by the use of Fourier transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (HNMR), and thermogravimetric analysis (TGA) to ensure the accuracy of the synthesis process and the appropriate thermal stability. The solution properties of the surfactant synthesized from linseeds, abbreviated as PELS, were analyzed through pH and the electrical conductivity at different concentrations. It must be regarded that micellar behavior is an essential parameter for each surfactant normally analyzed with surface tension (ST) and interfacial tension (IFT) respectively expressing 96% (28.97 to 0.99) and 59% (74.5 to 28) optimization. The fact that all of these experiments indicate the value of 1500 ppm as the critical micelles concentration must be taken into consideration. The wettability alteration was analyzed through a contact angle experiment on the sandstone surface showing a 58% optimization once the contact angle reduced to 54.5° in the water-wet zone. Owing to the presence of salt in the reservoir condition, NaCl was utilized as a sample to analyze the ion effect on the PELS performance. Meanwhile, it demonstrated good compatibility, especially in IFT reduction, reducing the IFT value from 0.99 in CMC point to 0.26 mn/m in the presence of NaCl ions. Several other surfactant properties, such as foamability, emulsion stability, and salt compatibility were analyzed for chemical enhanced oil recovery purposes. The adsorption of surfactant molecules on the rock surface reduces the surfactant efficiency and is of significant importance. This issue was evaluated and the pertinent results were compared with common models of isotherm absorption. Ultimately, the results of core flooding experiments using sandstone sample illustrated a 7.9% increase in the recovery factor and the required relative permeability charts were plotted via JBN method.

Microbially induced sedimentary structures from the Xinji Formation (Cambrian Series 2), Western Henan, North China

Abundant well‐preserved microbially induced sedimentary structures (MISS) are exposed in the Xinji Formation, the earliest Cambrian sedimentary unit in North China. The MISS herein are categorized into microbial mat growth structure (wrinkle structures and mat biolaminites) and microbial mat destruction structure (sand cracks and ‘Manchuriophycus’ structures). The MISS developed on the surface of thick quartz sandstones, as well as the lithologic interface between thin sandstone and mudstone. Most of the sand cracks lack the direct evidence of microbial activities, whereas the mat biolaminites that consist of filamentous mica, clay minerals, and quartz grains may record the in situ microbial mats. The Xinji Formation deposited along with the Cambrian explosion when biodiversity and abundance of metazoan stayed relatively low. Besides, the intermittently exposed tidal flats are not the ideal place for early life, which exacerbated the ecological vacuum therein. The massive occurrence of the MISS in the siliciclastic rocks of the Xinji Formation indicated that the tidal flat setting during this period was still beneficial for accumulations of microbial mat because of the deficient grazing metazoans and weak bioturbation.

Natural surfactant for sustainable carbon utilization in cleaner production of fossil fuels: Extraction, characterization and application studies

In this study, the extraction, characterization, and performance evaluation of a green surfactant, derived from bio-resource (Fenugreek seeds), is reported for effective carbon utilization in subsurface applications. Several characterization tools such as Fourier-transform infrared spectroscope, ultraviolet–visible spectroscope, methylene blue active substance test, surface tension tests, and scanning electron microscope were used to confirm saponin (surface activity) in synthesized surfactant and suitably compared with the properties of conventional surfactants in literature. The prepared green surfactant exhibited anionic behavior as validated by elemental analysis and adsorption studies. The critical micellar concentration of surfactant was determined by surface tension and electrical conductivity and its value was found to be around 0.2 wt%. Carbon dioxide absorption potential of green surfactant was envisaged by molality tests which confirmed that carbon dioxide absorption rate of surfactant was 7–18% higher than pure water. As a result, the surfactant showed high foam volume (> 40 ml) and foaming stability (8–10 h). The high temperature performance was also better. At 90 °C, carbon dioxide bubbles of larger size were present in sufficient quantity which indicated that foaming potential of surfactant was not severely affected by temperature. During adsorption studies, the green surfactant solution showed a mass-loss of 48–60% on a sandstone surface, which is better than the one of a conventional surfactant. It also showed superior property than conventional surfactants in adsorption isotherm investigations. Thus, the use of these green surfactants in subsurface scenario for carbon utilization and oil recovery from a porous media is recommended.

Accelerated disintegration of in situ disconnected portions of sandstone outcrops

Sandstone weathering/disintegration is a complex process involving loose material production, rockfall phenomena, and creation of picturesque natural sceneries. On historical monuments, they induce damage to building stone. Here we present a new look on sandstone weathering/recession the central aspect of which is rapid disintegration of portions of the rock massif, which are no longer physically connected with the main rock mass, though still in situ. A set of field and laboratory measurements including mechanical (tensile strength, drilling resistance) and hydraulic (permeability, surface moisture) methods were applied to compare the properties of the disconnected portions with those of the surrounding rock mass. Also, physical weathering experiments were performed to characterize the effect of confinement on the breakdown rate of several sandstone samples. The presence of disconnected portions is very common in dry climates where they are usually elongated parallel to horizontal surfaces. In humid temperate climates, however, they are less abundant, being elongated mostly vertically. The surfaces of disconnection follow bedding planes, planar elements of other sedimentary structures, and subhorizontal fractures, and stress shadows on subvertical cliff faces. Weathered surfaces of the disconnected portions show reduced tensile strength and drilling resistance values, a faster capillary water absorption and a higher surface moisture compared to the much less weathered surfaces of the surrounding rock mass. Physical experiments demonstrated that a confinement by the surrounding rock mass may considerably delay the loosening of rock during weathering. The much faster disintegration rates of the disconnected portions of rock compared to their surroundings are explained by the fact that they are not confined and have a larger surface area. The recession rates of sandstone surfaces with disconnected portions are highly variable both in space and time and their genesis can be demonstrated by two suggested conceptual models.

Formulation of Environmentally Safe Graffiti Remover Containing Esterified Plant Oils and Sugar Surfactant

The removal of graffiti or over-painting requires special attention in order to not induce the surface destruction but to also address all of the important eco-compatibility concerns. Because of the necessity to avoid the use of volatile and toxic petroleum-based solvents that are common in cleaning formulations, much attention has recently been paid to the design of a variety of sustainable formulations that are based on biodegradable raw materials. In the present contribution we propose a new approach to graffiti cleaning formulations that are composed of newly synthesized green solvents such as esterified plant oils, i.e., rapeseed oil (RO), sunflower oil (SO), or used cooking oil (UCO), ethyl lactate (EL), and alkylpolyglucosides (APGs) as surfactants. Oil PEG-8 ester solvents were synthesized through the direct esterification/transesterification of these oils using monobutyltin(IV) tris(2-ethylhexanoate) and titanium(IV) butoxide catalysts under mild process conditions. The most efficient formulations, determined by optimization through the response surface methodology (RSM) was more effective in comparison to the reference solvents such as the so-called Nitro solvent (denoting a mixture of toluene and acetone) and petroleum ether. Additionally, the optimal product was found to be effective in removing graffiti from glass, metal, or sandstone surfaces under open-field conditions in the city of Wrocław. The performed studies could be an invaluable tool for developing future green formulations for graffiti removal.

Quantitative evaluation of alteration and exfoliation in Jurassic sandstone, Chongqing Danzishi rock carvings, China

Historical relics of Jurassic sandstones in southwest China have been subjected to weathering damage. Exfoliation, characterized by the detachment of multiple thin stone layers sub-parallel to the stone surface, is common in sandstone heritage sites. However, its mechanism of action remains poorly understood. In this study, a conceptual model of exfoliation is drawn from the literature and field investigations. To quantitatively determine the exfoliation mechanism, a range of non-destructive field-based methods (surface hardness, water absorption test, roughness, and amplitude of residual spalling layers) and laboratory analyses (scanning electron microscopy (SEM) and X-ray diffraction (XRD)) are adopted as weathering agents for separated detachments. In addition, the grain and pore sizes of weathering products are analyzed using digital image techniques. The results show that the roughness, water absorption coefficient, and pore size in sandstone surfaces increase from the inner layer to the outer layer, and their hardness and grain size decrease, respectively. The proportions of quartz, dolomite, and illite increases from the interior to the exterior, whereas the proportion of feldspar decreases correspondingly. The residual column strip structure derived from feldspar alteration and a mixed montmorillonite-illite mineral layer can be observed in the SEM images. It can be inferred from surviving environmental analysis that comprehensive actions from solar radiation, acid rain attack and capillary rise lead to sandstone exfoliation. In addition, the alteration of feldspar plays an important role during sandstone exfoliation. The results of this study enhance our understanding of the exfoliation of the Jurassic sandstone of the Chongqing Danzishi rock carvings in China.

Experimental study of one-step economical retarded sandstone acid

The objective of this study is to experimentally evaluate a new acid combination of HEDP: CH3COOH as a retarded acid to minimize some limitations of high-temperature sandstone acidizing, such as fast acid-rock reaction and secondary precipitation pipeline corrosion. In this work, the acid–base titration, core-powder solubility test, scale deposition test, corrosion rate measurement and corefloods were carried out to evaluate the performances of the acid combination, including acidity characteristics, retarded performance, preventing scale rate, corrosivity and improving permeability. And then the microstructure and mineral content in sandstone samples were observed and analyzed with SEM–EDS. The results of evaluation tests indicated that the new acid combination has excellent performances on retarded rate, preventing scale deposition, permeability enhancement and lower corrosivity, comparing with conventional mud acid. The results of SEM and EDS showed that the microstructure and mineral content of sandstone changed after acid treatment. Compared with mud acid, the new acid system can react more with small particles on sandstone surface and less with the skeleton of samples and the decrease in the contents of Mg, Al, Na, K, Ca and Fe is relatively lower.

Bacterial and fungal communities in the sandstone biofilms of two famous Buddhist grottoes in China

Microorganisms can accelerate the deterioration of stone monuments. In this study, we used next-generation sequencing (Illumina MiSeq PE300 Platform) to investigate the microbial biofilm communities that have developed on sandstone in two famous Buddhist cave temples, the Maijishan Grottoes and Tiantishan Grottoes, located on the historical Silk Road in western China. We found high bacterial diversity and relatively low eukaryota diversity based on 16S and 18S ribosomal RNA (rRNA) sequencing analysis. The dominant bacterial groups were Cyanobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, and Chloroflexi. The dominant eukaryota were Ascomycota, Basidiomycota, and Chytridiomycota. The most dominant genes among the bacteria were from Cyanobacteria (unclassified and no rank), Pseudonocardia, Kribbella, and Rubrobacter; the dominant fungal genes were from unclassified Lecanorales and Capnodiales (unclassified and norank). These microbes form biofilms that will contribute to biodeterioration of the underlying sandstone. Combining with field monitoring and microscopic analysis, we determined that high bioreceptivity of the sandstone and locally available water were two important exogenous and endogenous factors that promoted microbial colonization, proliferation, and subsequent biofilm formation. The aforementioned microbes usually coexisted on the sandstone surfaces by building an inter-connected and dynamic community capable of adapting to and resisting the harsh local environmental conditions to survive and undergo succession.

Late Cretaceous Dinosaur Tracks from the Iron Springs Formation, Iron County, Utah

Located in Iron County, Utah, the Parowan Gap dinosaur track site contains over one hundred natural casts of non-avian dinosaur tracks preserved in sandstones and siltstones of the Late Cretaceous (≈83 Ma) Iron Springs Formation. For this study, the authors returned to the area to survey for and describe previously unidentified tracks. Many tracks from this new study occur as in situ casts found on the basal surfaces of sandstones deposited by braided and meandering rivers on the coastal plain of the Western Interior Seaway, with some specimens from fallen talus blocks. Over the course of two years, the research team identified and recorded a total of 31 specimens. The results comprise tracks that resemble a minimum of at least five ichnotaxa including Caririchnium, Amblydactylus, Ceratopsipes, Magnoavipes, and Dromaeosauripus. The most common and well-recognized ichnogenus recorded in the Iron Springs Formation is Caririchnium, which likely represents ornithopod dinosaurs. We also identified two Ceratopsipes tracks in a fallen sandstone block. The pair of tracks are significant because they are the second set from the ichnotaxa found at Parowan Gap. Together the Parowan Gap Ceratopsipes samples represent the oldest ceratopsian tracks in Utah. The potential Dromaeosauripus specimen represents a small theropod dinosaur. This specimen is of great interest because theropod tracks, especially dromaeosaur tracks, are less common in the Iron Springs Formation, with a total of seven tracks reported from previous studies. If this is an appropriate interpretation, it would make the potential Dromaeosauripus track the youngest dromaeosaur trace fossil in Utah.

Critical micelle concentration, interfacial tension and wettability alteration study on the surface of paraffin oil-wet sandstone using saponin

Nowadays, the implementation of chemical enhanced oil recovery (CEOR) techniques improves the oil recovery by injecting synthetic surfactants in reservoir. However, the recent use of this synthetic surfactant is quite expensive and possesses toxicity problems when exposed to the environment. This issue has forced the search for alternative, cheaper and natural synthetic surfactant to enhance oil recovery. Hence, this study aims to provide some insights into the effect of saponin as natural plant-based non-ionic surfactant on the surface of paraffin oil-wet sandstone. The effectiveness of saponin depends on the critical micelle concentration (CMC), interfacial tension (IFT) and wettability alteration. The surfactant concentration containing saponin was varying from 0.005wt% to 0.07wt% to determine CMC value using surface tension measurement, meanwhile for IFT measurement was conducted at 0.5wt% to 8wt% concentration using Krus Tensiometer K6. The experiments were conducted at standard condition with 25°C and 14.7psia. The findings showed that surface tension for CMC value of saponin is 0.05wt%. Approximately 27% reduction from initial IFT was achieved with 8wt% of saponin concentration. The saponin successfully alter the wetting state of oil-wet sandstone to intermediate-wet through quantitatively measurement of contact angle. Saponin with low CMC value is favourable to become a reference concentration as natural surfactant, effective to alter of reservoir rock properties, facilitate oil mobilization, increase oil recovery and suggested as an additive for mitigating wax deposition.

Experimental investigation and two-phase flow simulation of oil and nanofluids on micro CT images of sandstone for wettability alteration of the system

This work provides an analysis of the effect of nanofluids on the wettability of sandstone for the application of enhanced oil recovery. The wettability of sandstone with brine and nanofluids of ZnO, BiFeO 3, and SrFeO 3 is studied experimentally using contact angle calculations. Also, the direct simulations for the displacement of oil with brine and nanofluids are carried out on a micro-CT scanned porous sandstone structure for the measurement of capillary pressure and relative permeability. Fluid properties such as viscosity and density of the nanofluids, brine, and oil to be used in simulations were obtained using viscometer and densimeter. The experimental results show that the contact angle of crude oil on the sandstone surface has a higher value for nanofluids as 125.89° for ZnO, 122.88° for BiFeO 3, and 104.98 for SrFeO 3 as compared to brine 28.66°, which means the wettability of the system changes from oil-wet to water-wet by the addition of nanofluids. The simulation results indicate that BiFeO 3 nanofluid has a greater tendency to change the wettability of porous medium as compared to brine, ZnO, and SrFeO 3 nanofluids, as it shows better values of relative permeability and capillary pressure. • Micro-CT imaging of sandstone samples and image processing is explained. • Mathematical model and boundary conditions for two-phase flow simulation are described. • Experimental calculations for fluid properties i.e. contact angle, viscosity and density. • Saturation profiles for two-phase flow of oil and brine/nanofluids are studied. • Relative permeability and capillary pressure curves are evaluated.

High Salinity and High Temperature Stable Colloidal Silica Nanoparticles with Wettability Alteration Ability for EOR Applications.

The stability of nanoparticles at reservoir conditions is a key for a successful application of nanofluids for any oilfield operations, e.g., enhanced oil recovery (EOR). It has, however, remained a challenge to stabilize nanoparticles under high salinity and high temperature conditions for longer duration (at least months). In this work, we report surface modification of commercial silica nanoparticles by combination of zwitterionic and hydrophilic silanes to improve its stability under high salinity and high temperature conditions. To evaluate thermal stability, static and accelerated stability analyses methods were employed to predict the long-term thermal stability of the nanoparticles in pH range of 4–7. The contact angle measurements were performed on aged sandstone and carbonate rock surfaces to evaluate the ability of the nanoparticles to alter the wettability of the rock surfaces. The results of static stability analysis showed excellent thermal stability in 3.5% NaCl brine and synthetic seawater (SSW) at 60 °C for 1 month. The accelerated stability analysis predicted that the modified nanoparticles could remain stable for at least 6 months. The results of contact angle measurements on neutral-wet Berea, Bentheimer, and Austin Chalk showed that the modified nanoparticles were able to adsorb on these rock surfaces and altered wettability to water-wet. A larger change in contact angle for carbonate surface than in sandstone surface showed that these particles could be more effective in carbonate reservoirs or reservoirs with high carbonate content and help improve oil recovery.